22 U.S. NATIONAL MUSEUM BULLETIN 2 84 



region and joins the pterotic canal (the latter canal is contained par- 

 tially in the sphenotic). 



Parietal (figs. 1, 3, 5). — The parietals contact each other only for 

 a very short distance, at the dorsal midline of the skull just anterior 

 to the large dorsomedian opening of the supratemporal canal of the 

 laterosensory system. Along most of their median borders the parietals 

 are separated from each other by the frontals anteriorly and by the 

 supraoccipital posteriorly. Just anterior to its posterior end, each pari- 

 etal bears a raised crest through which the supratemporal canal passes 

 (there are three external openings to this canal in each parietal). 

 DorsaUy each parietal crest curves anteriorly and is continuous with 

 the anteriorly extending dorsal crest of the parietal's respective frontal. 

 Just before the parietal crest curves anteriorly it also joins a raised 

 portion of the supraoccipital that forms the posteriormost border of 

 the large dorsomedian opening of the supratemporal canal of the 

 laterosensory system. The crest of each parietal is continuous ventro- 

 laterally with the crest of its respective pterotic. The posterolateral- 

 most end of each parietal crest forms the anterior border of an ex- 

 ternal opening of the supratemporal canal. The posterior border of 

 each opening is formed by its respective epiotic (anterior margin of 

 the raised process that articulates with the posttemporal). The canal 

 in each parietal crest is continuous with the canal in the mesially 

 extending arm of its respective lateral extrascapular. There are no 

 median extrascapulars. 



Each parietal contacts its respective pterotic laterally. Postero- 

 laterally each parietal fits into a deep groove between the bladelike 

 and pyramidally shaped portions of its respective pterotic. The 

 portion of the parietal continuing anteriorly from the groove is over- 

 lapped externally by the bladelike portion of the pterotic alone. 

 Ventrolaterally each parietal overlaps the dorsoposteriormost exten- 

 sion of its respective sphenotic. 



On the internal surface of the parietal is a shallow groove con- 

 tinuous ventrally with a similar groove in the sphenotic. The anterior 

 vertical semicircular canal of the ear lies in this groove. 



Pterotic (figs. 1-5). — Each pterotic is an irregularly shaped bone 

 with a heavy-bodied and roughly pjrramidaUy shaped, hollow, 

 posterior section (forming the posterodorsolateral corner of the skull) 

 and a long, thin, bladelike anterior section. The internal perimeter 

 of the pyramidal section is a roughly ringlike jointing surface that 

 lies internal to, and is separated by a deep groove from, the dorsally 

 lying bladelike section. Sandwiched m the groove between these 

 two pterotic portions is the posterolateral region of the parietal. 

 The parietal extends anteriorly beyond the level of the groove and 

 lies under the pterotic bladelike portion. 



